Postero-anterior and lateral chest x-rays
In patients with pectus excavatum the heart is displaced dorsally and often "squeezed" between the depressed sternum and the spine. This causes the cardiac silhouette to be shifted to the left and can give the impression of cardiomegaly. The left heart border becomes straightened as a result, and the main pulmonary trunk can look enlarged.
The right heart border may bulge to the right if the heart is compressed against the spine, but is usually displaced to the left. Ill-defined shadowing in the right cardio-phrenic angle gives the impression of right middle lobe pathology, but does not show an air bronchogram. Its cause is the tissues of the anterior chest wall projected over the lung adjacent to the right heart.
Clues as to the presence of pectus excavatum on the PA radiograph are the easy visibility of the thoracic vertebral bodies and inter-vertebral discs through the heart shadow (as the heart is displaced to the left) and horizontal posterior ribs with downward sloping anterior ribs (giving a "7" and "reverse-7" configuration). Clinical examination of the patient will confirm the presence of a depressed sternum. A lateral radiograph demonstrates the sternal depression, which varies from minor sternal flattening causing slight reduction in the AP diameter of the chest to marked sternal depression and compression of the heart against the spine. The lateral radiograph also confirms the absence of right middle lobe disease and cardiomegaly.
Rarely pectus excavatum is associated with mitral valve prolapse and patients with Marfan's syndrome may have pectus excavatum.
 Raphael MJ, Donaldson RM. The normal heart: methods of examination (Volume 1, Chapter 21). In Sutton D (Ed) A Textbook of Radiology and Imaging, Sixth Edition. Churchill Livingstone, New York, pp 541-66 (1998).
 Meholic A, Ketai L, Lofgren R. Chest Wall (Chapter 14). In Fundamentals of Chest Radiology. WB Saunders Company, Philadelphia, pp 221-34 (1996).